The present invention relates to a surface state monitoring method and apparatus for performing in-situ monitoring of surface states of semiconductor substrates by infrared spectroscopy at fabrication sites of semiconductor devices.
Various requirements at fabrication sites of semiconductor devices require surface states of the semiconductor substrates being accurately grasped.
To give an example, in the field of semiconductor integrated circuits of memory devices, such as DRAM (Dynamic Random Access Memory), etc., and of logic devices, to form a gate insulation film having dielectric breakdown voltage of a required value, it is very important that surface states of a semiconductor substrate are administered. As a device has higher integration, the gate insulation film at the time of the fabrication of the device is made thinner, and the device has a design that the function for insulating an electric field (about 4xc3x97106 V/cm) of a MOS (Metal Oxide Semiconductor) FET (Field Effect Transistor) in operation has a small margin. Generally, a gate insulation film is formed by thermal oxidation. In forming a gate insulation film by thermal oxidation, in a case of surface contamination, as of metal contamination, chemical contamination, organic contamination or others is present, there is a risk that dielectric breakdown of the formed gate insulation film may be induced. It is known that organic contaminants stayed on the substrate surfaces after the gate insulation film has been formed results in insulation deterioration.
Plasma etching is widely used in steps of patterning device structures. In the plasma etching process, to set optimum plasma etching conditions and to detect the end point of the plasma etching, it is very effective to know adsorption states, chemical bonding states, structures and thicknesses of reaction layers, etc. of surface states of semiconductor wafers. The plasma etching process is determined by dynamic balance in adsorption, reaction and elimination processes between influxes of radical ions, etc. fed in gas phase and outfluxes from semiconductor substrate surfaces.
Recently, semiconductor devices have elements increasingly micronized, and are made increasingly three dimensional. This makes it difficult for cleaning solutions to intrude into micronized regions or steep steps or to be replaced there. In consideration of future further micronization, dry cleaning is noted. For example, to remove organic contaminants staying on silicon substrates reaction with ozone or oxygen excited by UV radiation is effective. Oxygen molecules are dissolved to oxygen atoms by light of a below 242 nm wavelength. The organic contaminants are oxidized by the oxygen atoms and solved into H2O, O2, CO, CO2, etc. of high vapor pressures. Organic bonds, such as Cxe2x80x94C, Cxe2x80x94H, Cxe2x80x94O, etc. can be dissolved by UV radiation. Thus, knowing surface states of semiconductor substrates is very important also to control parameters for the dry cleaning, such as an optimum amount of radiation, wavelength, oxygen amount, etc.
Native oxide films formed on the surfaces of silicon substrates are not usable in devices because their thickness cannot be controlled. Accordingly, it is preferable that when a device is fabricated on a silicon substrate, native oxide film on the silicon substrate is removed, and silicon bonds on the surfaces are terminated with hydrogen to stabilize the surfaces of the silicon substrate. This is because hydrogen can be eliminated at a relatively low temperature of about 500xc2x0 C., and the termination with hydrogen relatively little affects the following processes. Most of silicon atoms on the surfaces of a silicon substrate subjected to UV ozone cleaning and hydrogen fluoride etching are terminated with hydrogen, and Sixe2x95x90H2 and Sixe2x80x94H are formed. Accordingly, if a state of the termination with hydrogen on silicon substrate surfaces, temperature dependency of the elimination of terminating hydrogen can be monitored, the silicon substrate surfaces at the start of semiconductor processing can be kept in a suitable state. Higher quality and higher yields can be expected.
Thus, it is very important to know a surface state of a semiconductor substrate in a fabrication process of a semiconductor device, and various monitoring methods and apparatuses have been proposed and locally practiced.
Means for monitoring a surface state of a semiconductor substrate by internal multiple reflection of infrared radiation is provided by, e.g., FT-IR (Fourier-transform spectroscopy) apparatus or the special use marketed by Perkin-Elmer Co., U.S.A. For wider applications of the means Graseby Specac Limited, for example, markets various accessories.
In the conventional surface state monitoring method using this means, as exemplified in FIG. 41A, a substrate-to-be-monitored 102 is cut into, e.g., a 40 mmxc3x9710 mm strip, and infrared radiation emitted from an infrared radiation source 104 is passed through the substrate-to-be-monitored 102 to monitor states of the substrate surfaces. Otherwise, as exemplified in FIG. 41B, a substrate-to-be-monitored 102 has the end tapered, and infrared radiation is incident on the end surface of the substrate-to-be-monitored 102 to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored. Otherwise, as exemplified in FIG. 41C, infrared radiation is incident on a substrate-to-be-monitored via a prism 106 positioned above the substrate to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored.
The basic principle of monitoring a surface state of a substrate by applying infrared radiation to a substrate to cause the infrared radiation to undergo multiple reflection inside the substrate is that spectra of frequency components of evanescent waves oozing when light reflects on the substrate surfaces are resonance-absorbed when they agree with molecular vibrational frequencies of organic contaminants on the substrate surfaces are measured, whereby kinds and amounts of the organic contaminants can be determined. The basic principle also has a function that information of organic contaminants on substrate surfaces is gradually made more exact. A signal vs. noise ratio (S/N ratio) is also improved.
However, these monitoring methods needs cutting a substrate-to-be-monitored into strips, additionally machining a substrate-to-be-monitored, or disposing a prism above a substrate-to-be-monitored. These monitoring methods have not been usable in the in-situ monitoring at site of fabricating semiconductor devices.
Methods of monitoring organic contaminants on semiconductor substrates are known thermal desorption GC/MS (Gas Chromatography/Mass Spectroscopy), APIMS (Atmospheric Pressure Ionization Mass Spectroscopy), TDS (Thermal Desorption Spectroscopy), etc. However, these methods are not suitable to be used in in-situ monitoring at site of fabricating semiconductors for reasons that these methods cannot directly observe large wafers of, e.g., above 300 mm-diameters which are expected to be developed, and need vacuum ambient atmosphere, and have low throughputs, and other reasons.
As described above, the above-described conventional surface state monitoring methods are not usable in the in-situ monitoring at site of fabricating semiconductor devices because the monitoring by these method is destructive, or these methods are not suitable for monitoring large semiconductor wafers. Surface state monitoring methods and apparatuses which permit the in-situ monitoring of substrate surfaces at site of fabricating semiconductor devices, and permit large wafers to be monitored have been expected.
An object of the present invention is to provide a surface state monitoring method and apparatus which enable, at the site of fabricating a semiconductor device, in-situ monitoring of surface states of a substrate-to-be-monitored by infrared radiation spectroscopy of internal multiple reflection.
The above-described object is achieved by a surface state monitoring apparatus comprising: a first infrared radiation condensing means for condensing infrared radiation emitted by an infrared radiation source on an outer peripheral part of a substrate-to-be-monitored and introducing the infrared radiation into the substrate-to-be-monitored; an incident angle control means for controlling an incident angle of the infrared radiation condensed by the first infrared radiation condensing means, which enters the substrate-to-be-monitored to be fixed to a prescribed value or to be variable; a second infrared radiation condensing means for condensing the infrared radiation which has undergone multiple reflection in the substrate-to-be-monitored and exits the substrate-to-be-monitored; an infrared radiation detecting means for detecting the infrared radiation condensed by the second infrared radiation condensing means; and an infrared radiation analyzing means for analyzing the infrared radiation detected by the infrared radiation detecting means to measure contaminants staying on the surfaces of the substrate-to-be-monitored. The surface state monitoring apparatus having this constitution enables a substrate-to-be-monitored to be monitored without being additionally processed for the monitoring and makes it unnecessary to cause infrared radiation to enter the substrate-to-be-monitored via a prism, etc. disposed above the substrate-to-be-monitored. The surface state monitoring apparatus is used as an apparatus for in-situ monitoring surface states of a substrate-to-be-monitored at the site of its fabrication by infrared spectroscopy.
In the above-described surface state monitoring apparatus it is possible that the incident angle control means controls an incident angle of the infrared radiation entering the substrate-to-be-monitored so that a reflection angle of the infrared radiation inside the substrate-to-be-monitored is below a total reflection critical angle.
In the above-described surface state monitoring apparatus it is possible that the incident angle control means controls an incident angle of the infrared radiation entering the substrate-to-be-monitored so that an energy reflectivity of the infrared radiation at the time of entering the substrate-to-be-monitored is below a prescribed value
In the above-described surface state monitoring apparatus it is possible that the infrared radiation analyzing means identifies the contaminants, based on a spectroscopic result given by Fourier transform spectroscopy.
In the above-described surface state monitoring apparatus it is possible that the infrared radiation analyzing means identifies the contaminants, based on a spectroscopic result given by infrared spectroscopy using a diffraction grating.
In the above-described surface state monitoring apparatus it is possible that the substrate-to-be-monitored has a pair of declined parts on outer peripheral parts, which are formed by chamfering the edges defined by a pair of surfaces of the substrate-to-be-monitored and the outer peripheral surface thereof, and the first infrared radiation condensing means condenses the infrared radiation on one or both of the pair of the declined parts of the substrate-to-be-monitored. Infrared radiation is introduced into a substrate-to-be-monitored through the declined parts formed in advance, so that infrared radiation can be introduced with high efficiency into the substrate-to-be-monitored without additionally processing the substrate-to-be-monitored. Infrared radiation is incident on both of the declined parts of a pair, whereby higher detection sensitivity can be obtained.
In the above-described surface state monitoring apparatus it is possible that the apparatus further comprises: a substrate mount including a position control mechanism for supporting the substrate-to-be-monitored and adjusting a position of the infrared radiation incident on the substrate-to-be-monitored, and a rotation mechanism for rotating the substrate-to-be-monitored. The substrate mount having this constitution makes the alignment of a substrate-to-be-monitored possible. The monitoring is repeated with the substrate-to-be-monitored being rotated. Surface states can be easily monitored all over the substrate surfaces.
In the above-described surface state monitoring apparatus it is possible that the first infrared radiation condensing means condenses the infrared radiation emitted by the infrared radiation source to an elliptical focus or a circular focus along an outer periphery of the substrate-to-be-monitored. Infrared radiation is condensed in an elliptical shape along an outer periphery of a substrate-to-be-monitored, whereby the infrared radiation can be used with higher use efficiency. Infrared radiation can be condensed into a circular shape to introduce the infrared radiation into a substrate-to-be-monitored but with a little lower use efficiency in comparison with that of the case that infrared radiation is condensed into the elliptical shape.
In the above-described surface state monitoring apparatus it is possible that the first infrared condensing means includes a spherical mirror, and an elliptical mirror positioned so as to position one focus of the elliptical mirror at a focus of the spherical mirror; the infrared radiation source is positioned at said one focus of the elliptical mirror; and the first infrared radiation condensing means condenses the infrared radiation emitted by the infrared radiation source to the other focus of the elliptical mirror.
In the above-described surface state monitoring apparatus it is possible that the second infrared radiation condensing means includes a spherical mirror, and an elliptical mirror positioned so as to position one focus of the elliptical mirror at a focus of the spherical mirror; the substrate-to-be-monitored is positioned so that an exit end surface of the substrate-to-be-monitored through which the infrared radiation exits is positioned at said one focus of the elliptical mirror; and the second infrared radiation condensing means condenses the infrared radiation exiting the substrate-to-be-monitored to the other focus of the elliptical mirror.
In the above-described surface state monitoring apparatus it is possible that the second infrared radiation condensing means includes a pair of reflecting mirrors which are opposed to each other with a gap therebetween on a side of the substrate-to-be-monitored being smaller than a gap therebetween on a side of the infrared radiation detecting means.
In the above-described surface state monitoring apparatus it is possible that the apparatus further comprises: a reflecting mirror disposed on an end surface of the substrate-to-be-monitored opposed to the end surface thereof on which the infrared radiation is incident, the reflecting mirror reflecting the infrared radiation exiting the substrate-to-be-monitored and introducing the infrared radiation again into the substrate-to-be-monitored. An optical path of infrared radiation propagating in a substrate-to-be-monitored can be long, so that higher detection sensitivity can be obtained.
In the above-described surface state monitoring apparatus it is possible that the substrate-to-be-monitored is a substrate having a pair of substantially parallel surfaces polished.
In the above-described surface state monitoring apparatus it is possible that the infrared radiation source includes a light source for emitting infrared radiation or near-infrared radiation, and an optical system for transforming light emitted by the light source into substantially parallel rays.
In the above-described surface state monitoring apparatus it is preferable that the substrate-to-be-monitored is a substrate which allows the infrared radiation to reflect more than 300 times in the substrate-to-be-monitored.
In the above-described surface state monitoring apparatus it is preferable that the substrate-to-be-monitored is monitored before being subjected to certain processing, after being subjected to certain processing or in certain processing.
The above-described object is also achieved by a surface state monitoring apparatus comprising: a first infrared radiation condenser for condensing infrared radiation emitted by an infrared radiation source on an outer peripheral part of a substrate-to-be-monitored and introducing the infrared radiation into the substrate-to-be-monitored; an incident angle controller for controlling an incident angle of the infrared radiation condensed by the first infrared radiation condensing means, which enters the substrate-to-be-monitored to be fixed to a prescribed value or to be variable; a second infrared radiation condenser for condensing the infrared radiation which has undergone multiple reflection in the substrate-to-be-monitored and exits the substrate-to-be-monitored; an infrared radiation detector for detecting the infrared radiation condensed by the second infrared radiation condensing means; and an infrared radiation analyzer for analyzing the infrared radiation detected by the infrared radiation detecting means to measure contaminants staying on the surfaces of the substrate-to-be-monitored.
The above-described object is also achieved by a surface state monitoring method comprising: condensing infrared radiation to an outer peripheral part of the substrate-to-be-monitored with an incident angle of the infrared radiation fixed to a required value or changed to introduce the infrared radiation into the substrate-to-be-monitored through the outer peripheral part; detecting the infrared radiation which has undergone internal multiple reflection in the substrate-to-be-monitored and exited the substrate-to-be-monitored; and analyzing the detected infrared radiation to measure contaminants staying on the surfaces of the substrate-to-be-monitored. The surface state monitoring method enables a substrate-to-be-monitored to be monitored without being additionally processed for the monitoring and makes it unnecessary to cause infrared radiation to enter the substrate-to-be-monitored via a prism, etc., disposed above the substrate-to-be-monitored. The surface state monitoring method makes it possible to in-situ monitor surface states of a semiconductor substrate at the site of its fabrication by infrared spectroscopy.
The above-described object is also achieved by a surface state monitoring method comprising: condensing infrared radiation to an outer peripheral part of a substrate-to-be-monitored, scanning incident angles in a prescribed range to introduce the infrared radiation into the substrate-to-be-monitored through the outer peripheral part; detecting the infrared radiation which has undergone internal multiple reflection in the substrate-to-be-monitored and exited the substrate-to-be-monitored; and analyzing the detected infrared radiation to measure contaminants staying on the surfaces of the substrate-to-be-monitored. The surface state monitoring method enables a substrate-to-be-monitored to be monitored without being additionally processed for the monitoring and makes it unnecessary to cause infrared. radiation to enter the substrate-to-be-monitored via a prism, etc. disposed above the substrate-to-be-monitored. The surface state monitoring apparatus is used as an apparatus for in-situ monitoring surface states of a substrate-to-be-monitored at the site of its fabrication by infrared spectroscopy. Incident angles of infrared radiation are scanned, whereby a region of a substrate-to-be-monitored along an infrared radiation optical path can be continuously detected. Higher detection sensitivity can be obtained.
In the above-described surface state monitoring method it is possible that the infrared radiation which has exited the substrate-to-be-monitored is subjected to Fourier transform spectroscopy, and the contaminants are identified based on a result of the spectroscopy.
In the above-described surface state monitoring method it is possible that the infrared radiation which has exited the substrate-to-be-monitored is subjected to the spectroscopy by using a diffraction grating, and the contaminants are identified based on a result of the spectroscopy.
The above-described object is also achieved by a surface state monitoring method comprising: condensing infrared radiation to an outer peripheral part of a substrate-to-be-monitored with an incident angle fixed to a prescribed value or changed to introduce the infrared radiation into the substrate-to-be-monitored through the outer peripheral part; detecting the infrared radiation which has undergone internal multiple reflection in the substrate-to-be-monitored and exited the substrate-to-be-monitored; and comparing an intensity of the detected infrared radiation with a reference intensity, and it is judged whether the substrate-to-be-monitored is good or not, based on a result of the comparison. Surface states of a substrate-to-be-monitored are thus monitored, whereby the surface states can be in-situ monitored at the site of its fabrication without additionally processing the substrate for the monitoring, causing infrared radiation into the substrate-to-be-monitored without the use of a prism, etc., disposed above the substrate-to-be-monitored. By the simple constitution of the apparatus, it can be judged whether or not a substrate-to-be-monitored is good.
The above-described object is also achieved by a surface state monitoring method comprising: condensing infrared radiation to an outer peripheral part of a substrate-to-be-monitored with an incident angle fixed to a prescribed value or changed to introduce the infrared radiation into the substrate-to-be-monitored through the outer peripheral part; detecting selectively that of the infrared radiation having undergone internal multiple reflection in the substrate-to-be-monitored and exited the substrate-to-be-monitored, which is in a wavelength range corresponding to a molecular vibration of a specific contaminant; and computing an amount of the specific contaminant staying on the surfaces of the substrate-to-be-monitored, based on an intensity of the detected infrared radiation. Surface states of a substrate-to-be-monitored are thus monitored, whereby it is not necessary to additionally process the substrate-to-be-monitored for the monitoring and cause infrared radiation to enter the substrate-to-be-monitored via a prism, etc., disposed above the substrate-to-be-monitored. This enables surface states of a semiconductor substrate to be in-situ monitored at the site of its fabrication. Amounts of contaminants staying on the surfaces of a substrate-to-be-monitored can be measured without the use of an infrared spectroscope, which makes the apparatus constitution simple and inexpensive.
In the above-described surface state monitoring method it is possible that the incident angle of the infrared radiation incident on the substrate-to-be-monitored is controlled in a range in which a reflecting angle of the infrared radiation in the substrate-to-be-monitored is larger than 0xc2x0 and not more than a total reflection critical angle. Loss of infrared radiation by the internal multiple reflection can be decreased.
In the above-described surface state monitoring method it is possible that an incident angle of the infrared radiation incident on the substrate-to-be-monitored is controlled in a range in which an energy reflectivity of the infrared radiation at the time of the infrared radiation entering the substrate-to-be-monitored is below a prescribed value. Use efficiency of the infrared radiation can be high.
In the above-described surface state monitoring method it is possible that the infrared radiation is caused to enter the substrate-to-be-monitored through one or both of a pair of declined parts on the outer peripheral part, which are formed by chamfering the edges defined by a pair of surfaces of the substrate-to-be-monitored and the outer peripheral surface thereof. Infrared radiation is introduced into a substrate-to-be-monitored through the declined parts formed in advance, so that infrared radiation can be introduced with high efficiency into the substrate-to-be-monitored without additionally processing the substrate-to-be-monitored. Infrared radiation is incident on both of the declined parts of a pair, whereby higher detection sensitivity can be obtained.
In the above-described surface state monitoring method it is possible that the infrared radiation which has entered the substrate-to-be-monitored is reciprocated in the substrate-to-be-monitored, exits the substrate-to-be-monitored through an end surface through which the infrared radiation has entered, and is detected. An optical path of the infrared radiation propagating in a substrate-to-be-monitored can be long. Higher detection sensitivity can be obtained.
In the above-described surface state monitoring method it is preferable that the substrate-to-be-monitored is a substrate having a pair of substantially parallel polished surfaces.
In the above-described surface state monitoring method it is possible that a position of a substrate mount for supporting the substrate-to-be-monitored is controlled so that an amount of the infrared radiation which is detected after the infrared radiation has undergone internal multiple reflection in the substrate-to-be-monitored is maximum.
In the above-described surface state monitoring method it is possible that the substrate-to-be-monitored is monitored several times, being rotated to monitor the surfaces of the substrate-to-be-monitored substantially all over the surfaces of the substrate-to-be-monitored.
In the above-described surface state monitoring method it is possible that the infrared radiation is condensed to an elliptical focus or a circular focus to be incident on the substrate-to-be-monitored. Infrared radiation is condensed to an elliptical shape along the outer periphery of a substrate-to-be-monitored, whereby the infrared radiation can be used with higher use efficiency. Infrared radiation can be introduced into a substrate-to-be-monitored by being condensed into a circular shape but with a little lower use efficiency in comparison with that of the case that infrared radiation is condensed into the elliptical shape.